Kotlin

Question

当我在另一个片段中更改 GameData 的 isInFavorites 属性时，我可以看到我的存储库的侦听器收到了更改，但是当我导航回该片段时，我的视图模型从未收到更新的值当我使用 MutableStateFlow.

奇怪的是，当我将流程更改为 MutableSharedFlow 时，突然间 viewmodel 也开始获取更新的值。有谁知道为什么会这样？我需要在这里使用 MutableStateFlow，但它不起作用。

存储库：

private val gameDataListResultMutableFlow: MutableStateFlow<Result<List<GameData>>> = MutableStateFlow(Result.Loading)



    override suspend fun observeGameDataList(): Flow<Result<List<GameData>>>
        {
   

      CoroutineScope(Dispatchers.IO + coroutineContext).launch {
                localGameDataSource.observeGameDataList().collectLatest{
                     if(it is Result.Success)
                     {
                        Timber.d("local data change favorite value of item 0: ${it.data[0].isInFavorites}")
                     }
               
                    gameDataListResultMutableFlow.emit(it)
                }
            }
    }

视图模型:

private suspend fun observeGameListResult()
{

    gameRepository.observeGameDataList().collect{

        if(it is Result.Success)
            Timber.d("data change received in viewmodel value of item 0: ${it.data[0].isInFavorites}")

        gameListResultMutableLiveData.postValue(it)
    }
}


fun getGameListResultLiveData(): LiveData<Result<List<GameData>>>
{
    launch(coroutineContext) {
        observeGameListResult()
    }

    return gameListResultMutableLiveData
}

使用 StateFlow 时的日志

LOADING THE INITIAL STATE, ISFAVORITE VALUE IS TRUE

D/DefaultGameRepository: local data change favorite value of item 0: true
D/GameListViewModel: data change received in viewmodel value of item 0: true



SWITCHING TO ANOTHER FRAGMENT TO CHANGE THE ISFAVORITE'S VALUE TO FALSE, WHICH IS RECEIVED ONLY BY 
THE LOCAL SOURCE LISTENER

D/DefaultGameRepository: local data change the favorite value of item 0: false



SWITCHING BACK TO THE INITIAL FRAGMENT AND THE UPDATED VALUE OF THE ISFAVORITE REFLECTED ON THE LOCAL SOURCE LISTENER BUT NOT ON THE VIEWMODEL LISTENER---

D/GameListViewModel: data change received in viewmodel value of item 0: true
D/DefaultGameRepository: local data change the favorite value of item 0: false

使用SharedFlow时的日志：

LOADING THE INITIAL STATE, ISFAVORITE VALUE IS TRUE

D/DefaultGameRepository: local data change the favorite value of item 0: true
D/GameListViewModel: data change received in viewmodel value of item 0: true
    

SWITCHING TO ANOTHER FRAGMENT TO CHANGE THE ISFAVORITE'S VALUE TO FALSE, WHICH IS RECEIVED BY LOCAL 
SOURCE AND THE VIEWMODEL LISTENER
        
D/DefaultGameRepository: local data change the favorite value of item 0: false
D/GameListViewModel: data change received in viewmodel value of item 0: false
    

SWITCHING BACK TO THE INITIAL FRAGMENT AND THE UPDATED VALUE OF THE ISFAVORITE REFLECTED ON THE 
VIEWMODEL   
 
D/DefaultGameRepository: local data change the favorite value of item 0: false
D/GameListViewModel: data change received in viewmodel value of item 0: false
D/GameListViewModel: data change received in viewmodel value of item 0: false

Answer 1

是的，所以主要原因可能是 MutableStateFlow 不会发出，除非要发出的建议对象不等于旧值。然而，MutableSharedFlow 将始终发出，因为它的发出逻辑没有 distinctUntilChanged() 等于逻辑。

来自 SharedFlow 文档：

Strong equality-based conflation

Values in state flow are conflated using Any.equals comparison in a similar way to distinctUntilChanged operator. It is used to conflate incoming updates to value in MutableStateFlow and to suppress emission of the values to collectors when new value is equal to the previously emitted one. State flow behavior with classes that violate the contract for Any.equals is unspecified.

https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/-state-flow/index.html

Kotlin - MutableStateFlow Emmision 从未收到

Kotlin - MutableStateFlow Emmision is Never Received

java

android

kotlin-coroutines

kotlin-flow